Legacy Status is given to all players who subscribed to FFXIV 1.x for at least 90 days. To qualify for a legacy account you must have subscribed for at least 90 days before June 30th, 2012
--Any player who paid for any cumulative 90 days between the commencement of billing services on January 6th, 2012 and the suspension of billing services on September 29th, 2012 qualified for Legacy status, regardless of which 90 days were purchased or whether they were purchased as part of a larger plan.
Snippets taken from Gamerescape which has a full page on the Legacy Campaign: https://ffxiv.gamerescape.com/wiki/Legacy_Campaign
All existing 1.0 characters should have been transferred - one of my lv10 alts was transferred and has a legacymark.